When the bar that turns the tattoo machine on is pressed without an O-ring in place it rattles and doesn't make a consistent humming noise. Once you insert the rubber O-ring into the tattoo machine it changes how the machine runs. The ring only takes a couple of seconds to install. After installing the O-ring the noise that is made by the tattoo machine doesn't rattle and it makes a consistent humming sound. The O-ring is a simple little piece that makes the machine run much smoother and consistent.